He was asked about his views by The Telegraph during a question and answer session which followed a speech marking 20 years since Mr Blair was elected Labour leader.

Asked if the Better Together – the pro-UK campaign – and the Labour leadership have done enough to save the Union in the upcoming Scottish referendum, Mr Blair said: "I hope so and I believe so."

He added: "I think the arguments of the Better Together campaign have got stronger as time has gone on. ... [Among] most people I have talked to there's some optimism about it."

His prediction of victory comes with the No campaign enjoying a 16-point lead over the Yes camp with less than two months to go, according to a recent poll of polls.

The independence campaign made up ground earlier this year but appears to need a significant swing in public opinion if it is to win separation on September 18.

Mr Blair's invisibility in the pro-UK campaign is a marked contrast to Gordon Brown, his successor at Number 10, who has made a series of high profile interventions on the issue.

It was under Mr Blair's premiership that the Scottish Parliament was created following a referendum on devolution, while the 61-year-old was born in Edinburgh and educated at Fettes College, a prestigious Scottish independent school.

Some critics from within Mr Blair's own party have blamed his leadership and toxic legacy for alienating Scottish Labour voters and spurring the rise of Mr Salmond's Scottish National Party.

In December 2012, the former primer minister promised to "play a part" in the campaign against Scottish independence during a lunch with political journalists in Westminster.

Asked if devolution had been a spur to the SNP’s drive to independence, he said: "No, I don’t believe it’s the spur to independence. If we had not done devolution, you would just have had this debate a lot earlier. It’s inevitable that it happens and you have just got to take it on and win it, which I hope and believe we will."

Speaking again in March 2013, Mr Blair told an audience in Edinburgh: "I think ultimately, for Scotland, being part of the UK is in Scottish interests, it is in English interests, it is in the interests of the UK as a whole, because it goes with the grain of history."

Yet since the turn of the year Mr Blair has ignored calls for Labour grandees to head north to help defeat Scottish independence.

While Lord (John) Reid, Mr Brown and Lord (George) Robertson – all Scottish-born cabinet secretaries who served under Mr Blair – have made major speeches on independence in recent months, the former prime minister has stayed away from the campaign trail.

A Scottish Labour source said there were no plans for Mr Blair to appear for the pro-UK campaign between now and September's vote.